1. Field of the Invention
The invention relates to control of a vehicular automatic transmission, and more particularly, control of an automatic transmission that is able to be manually shifted in response to an operation by a driver.
2. Description of the Related Art
A vehicle is known which has an automatic transmission that is controlled according to one of a plurality of shift positions including a forward drive (D) position, a park (P) position, a reverse (R) position, and a neutral (N) position and the like. When such a vehicle is running in the D position, the automatic transmission shifts based on the state of the vehicle (e.g., vehicle speed, accelerator operation amount, and the like) according to a shift map stored in advance, irrespective of the intentions of the driver (hereinafter, this kind of shift may also be referred to as an “automatic shift”). In recent years, there have also come to be automatic transmissions that not only shift automatically, but which also allow the driver to shift as he or she desires by operating a switch or lever (hereinafter such a shift may also be referred to as a “manual shift”). Japanese Patent Application Publication No. 8-210495 (JP-A-8-210495), for example, describes technology that executes a shift command by a driver while preventing the engine from overspeeding (overrevving) or stalling in a vehicle provided with an automatic transmission in which such a manual shift is possible.
The control apparatus described in JP-A-8-210495 is a vehicular automatic transmission control apparatus that controls shifting in the automatic transmission based on the output from a vehicle speed detecting portion that detects a value indicative of the vehicle speed and the output from an engine load detecting portion that detects a value indicative of the engine load. This control apparatus includes a shift command portion that outputs a predetermined shift command in response to a manual operation, a region setting portion that sets a shift-allowed region in which a shift command output by the shift command portion is allowed to be executed and a shift-prohibited region in which a shift command output by the shift command portion is prohibited from being executed, and a delay portion that executes a shift command when the state of the vehicle moves into the shift-allowed region within a predetermined period of time after the shift command portion outputs a shift command when the state of the vehicle is in the shift-prohibited region. Incidentally, when a shift switch is operated three or more times in succession, the control apparatus stores the first two operations and ignores the rest.
As described above, the control apparatus described in JP-A-8-210495 delays execution of a shift command when the shift command is output while the state of the vehicle is in the shift-prohibited region and then executes that shift command if the state of the vehicle moves into the shift-allowed region within a predetermined period of time after that shift command is output. Accordingly, not only can the engine be prevented from overrevving or stalling if an inappropriate shift command is given, but the shift command by the driver can also be executed as quickly as possible without the driver having to perform the operation again.
However, the control apparatus described in JP-A-8-210495 has the following problem when a downshift is performed a plurality of times within a short period of time. That is, if the shift switch is operated three or more times in succession, the third and subsequent times are all ignored even if the state of the vehicle is such that the engine will not overspeed, which may bother the driver. Furthermore, all of the determinations of whether to allow or prohibit a shift are made at the time the shift operation is performed. As a result, even if the second shift is allowed, the engine may overspeed when that shift is executed if the vehicle speed, increases as a result of the accelerator being depressed while the first shift is being executed after the shift operation is performed, for example. Moreover, when the second shift output is prohibited, the second shift determination is already made so the second shift will be executed after delaying the shift output until the state of the vehicle moves into the shift-allowed region as a result of the accelerator being released or the vehicle speed decreasing. Therefore, there is a longer time lag between the time that the shift operation is performed and the time that the second shift is executed, which may bother the driver.